THE Victorian government has announced a $100 million boost to Melbourne's busiest rail services while warning the upcoming state budget will be a tough one.

Premier Denis Napthine announced the cash injection for the southeastern Frankston line, which carries about 60,000 people every weekday, as part of Tuesday's 2013-14 state budget.

He said the government was building for growth despite falling GST revenues from the federal government.

"We are managing the budget in difficult, challenging times, in times where we have a reduction in GST revenues," he told reporters.

"But at the same time doing it in a responsible, economic manner and that's what you'll see in the budget on Tuesday."

The extra money announced on Sunday would pay for track, signalling and power upgrades and allow the line to accommodate the newer X'Trapolis trains, Dr Napthine said.

He brushed off suggestions the boost was aimed at politically important seats on the line.

"Investing $100 million in the Frankston line will certainly show we care about people along the Frankston line," he said.

"Everybody who uses the metro rail system is important to us as a government."

Poor service on the Frankston line was a key issue in the 2010 election, with a swathe of seats along the line, including Bentleigh, Mordialloc and Carrum, switching from Labor to the coalition.

Dr Napthine also announced a funding injection of $224 million for disability support in the budget, which will take annual disability funding to $1.6 billion.

The funding provides $107 million for 720 new Individual Support Packages for people with high support needs, which will be partly funded by increased lodging fees for government-run disability accommodation.

The announcement comes after Victoria became the fourth state to sign up to the national disability care scheme on Saturday, agreeing to a statewide disability care program by the end of the decade.

The state government also announced budget funding on Sunday to buy land for a new primary school in Melbourne's south.

Education Minister Martin Dixon said the Ferrars Street school in South Melbourne would cater to the area's fast-growing population.

A spokesman for Mr Dixon said the government had not released the funding amount as negotiations were continuing over the sale.

The money comes on top of $11.5 million announced on Saturday for the first stage of a high school in Melbourne's outer north.

Last week the government announced three new schools would be built in growth areas in the city's west.

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